This disclosure relates generally to high temperature articles with an environmental barrier coating and a bondcoat with enhanced temperature capability. More particularly, this disclosure relates to high temperature ceramic matrix composite articles with an environmental barrier coating and a bondcoat that are configured to form, and/or include, an amorphous and devitrification resistant thermally grown oxide region, and methods of forming same.
High-temperature materials, such as, for example, ceramics, alloys, and intermetallics, offer attractive properties for use in structures designed for service at high temperatures in such applications as gas turbine engines, heat exchangers, and internal combustion engines, for example. However, the environments characteristic of these applications often include reactive species, such as water vapor, which at high temperatures may cause significant degradation of the material structure. For example, water vapor has been shown to cause significant surface recession and mass loss in silicon-bearing materials. The water vapor reacts with the structural material at high temperatures to form volatile silicon-including species, often resulting in unacceptably high recession rates.
Environmental barrier coatings (EBC's) are applied to silicon-bearing materials and other materials susceptible to attack by reactive species, such as high temperature water vapor; EBC's provide protection by prohibiting contact between the environment and the surface of the silicon-bearing substrate. EBC's applied to silicon-bearing substrates, for example, are designed to be relatively stable chemically in high-temperature, water vapor-including environments. One exemplary conventional EBC system, as described in U.S. Pat. No. 6,410,148, includes a silicon or silica bond layer (also referred to herein as a “bondcoat”) applied to a silicon-bearing substrate; an intermediate layer including mullite or a mullite-alkaline earth aluminosilicate mixture deposited over the bond layer, such as a silicon bond layer; and a top layer including an alkaline earth aluminosilicate deposited over the intermediate layer. In another example, U.S. Pat. No. 6,296,941, the top layer is a yttrium silicate layer rather than an aluminosilicate.
The above coating systems can provide suitable thermal and environmental protection for articles in demanding environments, but opportunities for improvement in coating performance exist.
Therefore, there is a need in the art for EBC systems for articles with improved temperature capabilities, and related articles and methods. Similarly, there is a need for ceramic matrix composite articles with environmental barrier coatings and bondcoats that include enhanced temperature capabilities, and related methods for making them.